SEOUL, April 17 (UPI) -- North Korea warned Thursday it would respond with "overwhelming deterrence" against the United States following Washington's deployment of B-1B strategic bombers to the Korean Peninsula for a joint air exercise with South Korea this week. The allies' drills represent an "open threat to the security of our state and a grave provocation that raises the military tension in the region to an extreme dangerous level," a spokesperson for North Korea's Defense Ministry said in